Obesity has become a major health problem worldwide and it’s an independent risk factor for adverse pregnancy outcome. The World Health Organization classifies obesity into class I BMI (body mass index) 30.0–34.9, class II 35.0–39.9, and class III 40 or greater.
The prevalence of obesity in the general population in the UK has increased markedly since the early 1990s. The prevalence of obesity in pregnancy has also been seen to increase, rising from 9%–10% in the early 1990s to 16%–19% in the 2000s. In England, where the prevalence of obesity in women is among the highest in Europe, one in five women of reproductive age are now obese (BMI ≥30 kg/m 2 ).
Pregnant women who are obese are at greater risk of almost all of early pregnancy-related complications compared with women of normal BMI, including;
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Maternal Complications:
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Infertility: threefold higher in obese than in nonobese due to ovulatory dysfunction and decreased insulin sensitivity.
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Maternal morbidity and mortality: 30% of maternal death were obese and 22% were overweight (2015 MBRRACE)
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First trimester miscarriage (OR 1.2)
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Recurrent miscarriage (OR 3.5)
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Venous thromboembolism: higher risk of pulmonary embolism (OR 14.9) than DVT (OR 4.4)
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Preeclampsia (risk doubled with each 5–7 kg/m 2 increase in prepregnancy BMI)
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Gestational hypertension (OR 2.5–3.5)
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Gestational diabetes (OR 2.6–4.0)
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Maternal infections (UTI OR 1.17, genital tract OR 1.24)
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Anaesthetic complications (25% of cardiac arrest in pregnancy is caused by anaesthesia, of those 75% are obese)
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Wound infection (OR 1.27)
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Depression (obese, 33.0%; overweight, 28.6%; normal weight 22.6%)
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Anxiety and eating disorder (OR 1.4)
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Serious mental illness
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Fetal Complications:
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Congenital anomalies (NTD OR 1.7 for obese, 3.11 for morbidly obese), other anomalies; hydrocephaly, cardiovascular, and limb reduction abnormalities
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Stillbirth (OR 3.8)
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Prematurity (<32 weeks OR 0.73)
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Macrosomia (>4000 g OR 1.7–1.9) (>4500 g OR 2.0–2.4)
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Neonatal death (OR 3.4)
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24.1
Management
24.1.1
Preconception and Early Pregnancy
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Counselling:
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Primary care specialists should counsel all women of reproductive age about the adverse effects of obesity on pregnancy outcome.
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Interventions:
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Clinical and population health practice should focus on interventions to reduce obesity in all women of reproductive age.
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Women with a BMI 30 kg/m 2 or greater wishing to become pregnant should be advised to take 5 mg folic acid supplementation daily, starting at least 1 month before conception and continuing during the first trimester of pregnancy.
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Obese women are at high risk of vitamin D deficiency. The evidence on whether routine vitamin D should be given to improve maternal and offspring outcomes remains uncertain.
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Venous thromboembolism risk assessment should be individually discussed, assessed, and documented at the preconception, first antenatal visit, during pregnancy, intrapartum, and postpartum. One third of pulmonary embolism occurs during the first trimester.
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Antenatal thromboprophylaxis should be considered based on the risk assessment.
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24.1.2
Antenatal
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Where?
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Care of women with obesity in pregnancy can be integrated into all antenatal clinics, with clear local guidelines and clinical pathways for care available. All pregnant women with a booking BMI 30 kg/m2or greater should be provided with accurate and accessible information about the risks associated with obesity in pregnancy and how they may be minimised. Women should be given the opportunity to discuss this information.
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Interventions:
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All pregnant women should have their weight and height measured using appropriate equipment, and their BMI calculated at the antenatal booking visit.
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An appropriate size of cuff should be used for blood pressure measurements taken at the booking visit and all subsequent antenatal consultations.
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There is a lack of consensus on optimal gestational weight gain. The Institute of Medicine guidelines (USA) recommend different ranges of weight gain for normal weight, overweight, and obese women. (BMI 18.5; recommended weight gain 12.5–18 kg), normal weight (BMI, 18.5–24.9; 11.5–16 kg), overweight (BMI, 25.0–29.9; 7–11.5 kg), and obese (BMI <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='≥’>≥≥
≥
30; 5–9 kg). These guidelines are the most widely used but are not adopted routinely in clinical practice in the UK.
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Dietetic advice by an appropriately trained professional should be provided early in the pregnancy with focus on a healthy diet rather than prescribed weight gain targets.
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Antiobesity or weight-loss drugs are not recommended for use in pregnancy.
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Pregnant women with a booking BMI 40 kg/m 2 or greater should be referred to an obstetric anaesthetist for consideration of antenatal assessment like difficulties with venous access, regional and general anaesthesia. Multidisciplinary discussion and planning should occur where significant potential difficulties are identified
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Women with more than one moderate risk factor (BMI of 35 kg/m 2 or greater, first pregnancy, maternal age of more than 40 years, family history of preeclampsia, and multiple pregnancy) may benefit from taking 150 mg aspirin daily from 12 weeks of gestation until birth of the baby.
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Antenatal screening:
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All women should be offered antenatal screening for chromosomal anomalies; Screening is less effective with a raised BMI.
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Screening for structural abnormalities between 18+0 and 20+6 weeks of gestation.
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Oral glucose tolerance test at 24–28 weeks. Consider early screening at 16 weeks in presence of other risk factors especially previous gestational diabetes.
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Women with a BMI 30 kg/m 2 or greater should be screened for mental health problems.
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Further reading
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